Aim: To assess the knowledge of patients hospitalized for cardiovascular co-morbidities in diabetes mellitus (DM), and its relationship to the confrontation and attitudes towards the disease. Method: This was a prospective cross-sectional study, conducted in the inpatient unit with cardiac patients affected by DM. Their level of knowledge about diabetes was assessed using the Diabetes Knowledge Scale (DKN-A) and the psychological and emotional aspects were assessed by use of the Diabetes Attitudes Questionnaire (ATT-19). Results: We included 220 patients with 63.0 ± 9.4 years, of which 119 (54.1%) were male. The punctuation of the scores ≥ eight in DKN-A was found in 55 patients (25%), and a score ≥ 60 on ATT-19 occurred in 37 patients (17.7%). Discussion: The patients who presented with relatively good knowledge about DM had a score of ≥ eight; those individuals who had a score ≥ 60 on the scale ATT-19 had an appropriate response to the disease. Conclusion: The patients generally had a low level of knowledge of DM and had difficulty in coping with the disease.